Electronic musical instrument with photoelectric switching



Dec. 5, 1961 M. D. CORWIN 3,011,379

ELECTRONIC MUSICAL INSTRUMENT WITH PHOTOELECTRIC SWITCHING Filed Feb. 5, 1957 INVENTOR. 41 /%1 ro/v .0. (b pmv,

ATTORNEYS.

3,011,379 ELECTRONIC MUSICAL INSTRUMENT WITH PHOTOELECTRIC SWITCHING Merton D. Corwin, Cincinnati, Ohio, assignor to The Baldwin Piano Company, Cincinnati, Ohio, at corporation of Ohio Filed Feb. 5, 1957, Ser. No. 638,386

6 Claims. (Cl. 84-119) The invention relates to polyphonic electrical musical instruments of the keyboard or organ type in which there is an electronic or other assembly of generators for producing electrical oscillations of frequencies appropriate for the notes of a musical scale. The outputs of such generators are sent to an amplifier and loud speaker system through switches operated by playing keys.

In one type of such instrument, the generators produce oscillations which are rich in harmonics, and various voices are produced by subjecting the oscillations to filter networks (selected by step tabs) on their way to the main amplifier and loud speaker. In advanced instruments of this sort, the playing keys are arranged each to operate a plurality of switches so that oscillations from a plurality of oetavely related generators can simultaneously be derived in different electrical headers, such as 4, 8', l6 headers and the like; and the outputs of these headers may be used alone or in combination to secure a wide variety of voices. This makes for a considerable multiplication and complexity of switching means.

In other instruments, where the generators produce simple or substantially sine wave oscillations, it is necessary to mix in varying amplitudes oscillations represen tative of the fundamental and the desired partials or harmonies for each note; and again each of the playing keys must operate a substantial number of switches.

Further, in advanced instruments of the organ type, it is desirable to provide for the gradual onset of the derived tones so as to avoid those surges of current which produce the eifect sometimes known as key clicks. This has led to the use of resistive switch structures, still further complicating and increasing the expense of key switch assemblies.

It is a fundamental object of this invention to provide a musical instrument with an improved key switching system which has all of the advantages of former mechanical systems, but is simpler and cheaper. Specifically, it is an object to provide a system which will handle and switch a plurality of circuits for each key and which will avoid key clicks, while being mechanically simple and more economical.

It is an object of the invention to provide means for the adaptation of photoelectric switching to electrical musical instruments.

It is an object of the invention to provide for the use of printed circuitry, and for the use of unitary assem- I blies of a plurality of photocells which are readily replaceable.

These and other objects of the invention which will be set forth hereinafter or will be apparent to one skilled in the art upon reading these specifications, are accomplished by that construction and arrangement of parts of which an exemplary embodiment will be disclosed herein.

Reference is made to the accompanying drawings wherein:

FIGURE 1 is an elevational view of a playing key and includes a sectional view of the switching apparatus.

FIGURE 2. is a partial longitudinal section of the switching apparatus taken along the section line 2--2 of FIGURE 1.

3,011,379 Patented Dec. 5, 1961 ice FIGURE 3 is a perspective view of one form of unitary photocell assembly.

FIGURE 4 is a side elevational view thereof.

FIGURE 5 is a partial plan view of a strip element for mounting photocell assemblies.

FIGURE 6 is a sectional view thereof taken along the section line 6-6 of FIGURE 5.

FIGURE 7 is a partial elevational view of the same structure from the other side.

FIGURE 8 is a partial elevational view of a printed circuit element for the reception of photocell assemblies taken from the face side.

FIGURE 9 is a sectional view thereof taken along the section line 9-9 of FIGURE 8.

FIGURE 10 is an elevational view of the same element taken from the reverse side.

FIGURE 11 is a sectional view showing another means for mounting photocell assemblies.

FIGURE .12 is a sectional view of an encapsulated, single crystal photocell such as may also be used in the invention.

FIGURE 13 is a perspective view of another form of photocell assembly, using the structures of FIGURE 12.

It has been found that the response of photocells of the types hereinafter disclosed is directly proportional to the position of a shutter element opposite an opening through which light from a suitable source can reach the photocell assembly. Thus, if such shutters are moved by means of playing keys, switching will be accomplished without key clicks. Various types of photocells using various semi-conductive materials may be employed. Clearly, the individual photocell units should have a high ratio of dark to light resistance. Preferably they have a low light resistance, but this is not necessary so long as they have the proper ratio. Thus, cells having a light resistance of as much as 5,000 ohms will be found suitable providing the dark resistance of the cells is of the order of 200,000 ohms or greater. An attenuation of about decibels is desirable in a key switch; but this is obtainable in photocells of the types hereinafter set forth. The specific semi-conductive material employed is not a limitation on the invention. By way of nonlimiting examples, attenuations greater than 80 decibels can be obtained with cadmium selenide photocells and with lead sulfide photocells.

Referring now to FIGURE 1, 1 represents the playing key of an electrical musical instrument pivoted in the usual fashion as at 3. It will be understood that the key will be provided with suitable stops to determine its non-operated and depressed positions, and that means will be provided for biasing the key to the non-operated position, although such means have not been shown in the figure. A simple shutterelement 4 in the form of an opaque strip is shown attached to the playing key, its rear end extending downwardly. This shutter operates between a housing 5 for a source of illumination 7 and a housing -8 for a series of photocell assemblies, one of which is indicated at 10. The housings may be made of any suitable light-opaque material, sheet metal being excellent for the purpose. The photocell assembly 10 in FIGURE 1 is shown as supported by a panel 11 of inisullative substance, which will hereinafter be more fully described. The housing 5 is provided with an opening 12 and the housing 8 is provided with an opening 13. These openings are in alignment with each other and with light source 7 and the photocell assembly 10. It will be readily understood from FIGURE 1 that as the playing end of the key 1 is depressed, the shutter 4 will be raised so as to uncover the openings 12 and 13, permitting light to pass from the source to the photocell assembly.

The switches of this invention are preferably made in the form of gangs. Thus, as is indicated in FIGURE 2, the housings and 8 are made in elongated form extending transversely of a series of playing keys making up a clavier or a part of it in the instrument. The light source 7 may be a continuous elongated member. Any suitable form of light source may be employed, a structure with an elongated filament or'a fluorescent tube, both being suitable. The gang switch assembly may be made if desired to extend either throughout the length of a particular keyboard or throughout some portion of that length, as for example, the length of one or two octaves therein. Thus, the gang assembly willbe provided with a plurality of shutters 4, 4a, etc., each attached to a different playing key and lying in spaced relationship in the narrow channel between the housings. vided with a series of openings 12, 12a, etc., and the housing 8 will be provided with a coacting series of openings 13, 13a, etc. The panel 11 will support a plurality of photocell assemblies 10, a, etc, In order to prevent cross-talk, the housing 8 will be provided with transverse opaque partitions 14, 14a, etc., lying between the photocell assemblies.

One exemplary photocell assembly is illustrated in FIGURES 3 and 4. It comprises a suitable insulative base 15, usually but not necessarily of glass or ceramic. This base bears conductive elements formed thereon by any of those procedures which are current for the manufacture of printed circuitry. Thus, a sheet of metallic foil may be adhered to one face of the base, the circuit elements printed thereon in a resistive ink, and the unprinted areas of the sheet etched away. Again the circuit ele ments may be deposited on the base by printing or by silk screen deposition. In the case of glass or ceramics, the printed circuit elements may be bonded to the base by a firing procedure.

In the form most clearly shown in FIGURE 3, the printed circuit elements comprise contact areas 16 and 16a, located near or at the upper and lower edges of the block, and extending tongues 17 and 17a. The elements are arranged in pairs, the elements of a pair having a contact area at opposite edges of the base, the tongues of the-elements being slightly spaced from each other and arranged parallel throughout a substantial width of the central portion of the base. Thus, one of the elements of a pair will have its contact area 16 located near the top of the base, while the other element of the pair will have its contact area 16a located near the bottom of the base. The tongue 17 of the first mentioned contact element projects downwardly while'the tongue 17a of the other contact element projects upwardly in spaced parallel relationship. The photocell is completed by covering the tongue portions of each pair of contact elements with a layer ofsemi-conductor or light-sensitive material. layer is indicated at 18. It may be a layer of cadmium selenide deposited in a furnace from a vapor phase, or it may be a layer of lead sulfide deposited from an aqueous medium.

The photocell assembly illustrated in FIGURES is shown as comprising four photocells. It is intended for an instrument in which the keys, or some of them at least, each operate four switches for the collection of four different electrical oscillations in suitable headers. assemblies may be made with lesser. or greater numbers of individual photocells in accordance with the requirements of particular uses. It is even possible to produce photocell assemblies of gang character which would be as long as the individual switch assemblies. This is not ordinarily preferred, since the ability to change photocell assemblies individually for the individual keys is preferred, not only in assembly, but also in replacement and repair.

In any photocell assembly, it is preferred that the coatings or layers 18 of photoelectric substance be kept electrically separated from each other so as to prevent crosstalk. This is readily accomplished by the employment Photocell The housing 5 will be pro- This 7 of amasking procedure during the deposition of the semiconductor.

The photocell assemblies are quite small. They have been illustrated as rectangular in form and having a width less than the normal width of the shanks of the playing keys in an instrument. The individual photocells in the assembly when made as indicated are also quite small. While dimensions do not constitute a limitation, the individual photocells may have active areas only about inch long and an inch wide.

In order to make use of printed circuitry, the preferred form of the insulative panel 11 is illustrated in FIGURES 8, 9 and 10. The panel is provided with holes 19, 20 etc., at the places Where the photocell assemblies are to be located. The panels may be of any suitable insulative substance including glass or ceramic, but are preferably made of laminated resinous materials capable of being readily drilled and stamped. On the face side of the panel, as shown in FIGURE 8, a series of printed circuitry conductors 21, 22, 23 and 24 are formed up to the edge of the perforation 19. Downwardly these conductors may terminate if desired in grommets, one of which is shown at 25, to which leads may be soldered for connection of the conductive elements to octavely or otherwise related generators. Above the perforation 19 another series of printed circuitry conductors is brought downwardly to the edge of the perforation. These conductors are indicated at 26, 27, 28 and 29. The conductors terminate upwardly in grommets, one of which is indicated at 30, the grommets being offset in lateral position. The opposite face ofthe panel may be provided with longitudinally extending conductive elements or headers 31, 3'2, 33 and 34 so located that a conductive element of each upper group on the face of the panel can be connected to one of the headers as by the grommet 30.

To each conductive element adjacent the perforation 19 there is attached a spring finger such'as 35 or 36 extending into the opening or perforation as shown. The fingers are made of any suitable springy conductive metal, such as, for example, beryllium copper. The fingers, when held in a suitable' jig, are readily attachable to the ends of the conductive elements of the series 21 to 24 and '26 to 29, as by soldering.

The holes 19, 20 etc. in the panel '11 are designed to receive the photocell assemblies 10. As will be evident from FIGURES 5, 6 and 7, the dimensioning of the photo" cell assembly and its printed'circuitry and the dimensioning and positioning of the spring fingers are such that the photocell assembly may be brought against the spring fingers so that each spring finger contacts individually one of the contact areas 16 or 16a of the photocell assembly; and the photocell assembly may be held in position from the rear by a larger spring finger 37 as will be evident from FIGURES 5, 6 and 7.

It will be evident that in the structures so illustrated the individual photocell assemblies are not only easily installed but are easily removable for repair or replace ment.

There are other ways in which photocell assemblies may be mounted to a panel. One of these is illustrated in FIGURE 11. Here the panel 11a is not perforated but instead is provided with spaced ribs 38 and 39 between which the photocell assembly 10 may be located and held by spring fingers, two of which are indicated at 40 and 41. This figure shows in dotted lines how phosingle, somewhat elongated crystal of photoelectric material, for example cadmium selenide. The crystal is physically and electrically joined at one end to a wire conductor 43 in a suitable way, as by means of a body 44 of dental amalgam. The other end of the crystal is contacted by a conductive spring 45 such as a spring of beryllium copper, by which it is electrically united with the opposite conductor wire 46. The crystal and adjacent parts of the structure are sealed suitably in a glass capsule 47 from which the leads 43 and 46 project. Other forms of encapsulated single crystal photocells are known. These structures may be made quite tiny, an exemplary structure which is excellent for the purposes of this invention having a glass capsule which is slightly less than A: inch in diameter and only about /2 inch long, the leads extending therefrom to any length suitable for the intended use.

Such photocells may be employed with panel structures such as those shown in FIGURES 8, 9 and 10 by soldering the leads of the photocells directly to the conductive elements of the series 21 to 24 and 26 to 29, the individual photocells when so mounted laid in spaced parallelism. The perforations 19 to in the panels 11 may be retained or dispensed with as desired.

It is also possible to mount series of such photocells on bases to be used precisely as described for the structures of FIGURES 3 and 4. This is illustrated in FIGURE 13 where a base 48 is employed, which again may be of glass or ceramic, but is preferably made of resinous laminate. Encapsulated photocells 49, 50, 51

and 52 are shown mounted in side by side relationship on the base, the leads of these photocells extending outwardly to positions adjacent the upper and lower edges of the base, where they are provided with contact elements. There are various ways in which this may be done. One convenient way is to bend over the ends of the conductors or leads and insert them in spaced holes adjacent the edges of the base. At the points of insertion each of these leads may be provided with a contact element in the form of a drop of solder, thus providing an upper series of contacts 53 and a lower series of contacts 54. The advantages of the use of photocell assemblies in manufacture, repair and replacement are thus retained; and the assemblies of FIGURE 13 may be mounted and used as hereinabove outlined in connection with FIGURES 5, 6, 7 and 11.

Modifications may be made in the invention without departing from the spirit of it. The invention having been described in certain exemplary embodiments, what is claimed as new and desired to be secured by Letters Patent is:

1. In an electrical musical instrument a playing key having actuated and unactuated positions, a plurality of generators for electrical oscillations including generators for harmonically related frequencies, and a switching means comprising a light source, a housing surrounding said light source, a series of photocells, a housing surrounding said series of photocells, said housings being located adjacent each other and provided with aligned openings so that light from said source can pass through said openings to reach all of the photocells in said series, and a shutter arranged to be moved by said key and coacting with said aligned openings to prevent illumination of said photocell series by light from said source when said key is in the unactuated position, and to permit concurrent illumination of the photocells in said series when said key is in the actuated position, each of the photocells in said series having a connection with separate but harmonically related generators in said plurality of generators, and also having connection with means for collecting said electrical oscillations for amplification and reproduction.

2. The structure claimed in claim 1 in which said series of photocells constitutes a photocell assembly removable individually from its housing.

3. The structure claimed in claim 1 in which there are a plurality of playing keys, in which both housings are elongated and extend transversely of said playing keys, in which the second mentioned housing contains a plurality of photocell series, there being one for each of said keys, and in which said second mentioned housing has transverse partitions between said photocell series, there being a shutter arranged to be moved by each such key upon actuation, whereby to illuminate from said light source a different one of said photocell series for each key, the individual photocells in each series being connected to harmonically related oscillators appropriate to the key for such series.

4. The structure claimed in claim 3, wherein said first mentioned housing contains a single elongated light source, common to the photocell series in said second mentioned housing.

5. The structure claimed in claim 4 wherein said photocell series are removably mounted with respect to an insulative panel.

6. The structure claimed in claim 4 wherein said photocell series are removably mounted with respect to an insulative panel, and wherein each photocell of a series has contact elements located adjacent opposite edges of a support upon which individual photocells of the said series are mounted, said panel having spring means for making contact with said contact elements individually.

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